Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $52.30   12.610%   $58.895   $58.90   $58.90   $58.90  
  Purchase #2 $182.89   10.856%   $202.7445   $202.74   $202.75   $202.70  
  Purchase #3 $84.65   3.578%   $87.6788   $87.68   $87.70   $87.70  
  Purchase #4 $130.56   5.652%   $137.9393   $137.94   $137.95   $137.90  
  Purchase #5 $92.52   11.346%   $103.0173   $103.02   $103.00   $103.00  
  Purchase #6 $229.48   6.208%   $243.7261   $243.73   $243.75   $243.70  
  Purchase #7 $11.96   13.301%   $13.5508   $13.55   $13.55   $13.60  
  7 purchase totals = $784.36       $847.5518   $847.56   $847.60   $847.50